1. Field of the Invention
The present invention relates to a radiation imaging apparatus and a radiation imaging system.
2. Description of the Related Art
Radiation imaging apparatuses having arrays of pixels in which switches such as TFTs (thin film transistors) and conversion elements such as photoelectric conversion elements are combined have been put to practical use as radiation imaging apparatuses used for medical imaging diagnosis and non-destructive examination by means of radiation such as X-rays.
In recent years, consideration has been given to increasing the functions of radiation imaging apparatuses. One way of increasing the functions that has been considered is including a function of monitoring the emission of radiation. For example, this function enables detection of the timing at which emission of radiation from a radiation source starts, detection of the timing at which the emission of the radiation is to be stopped, and detection of the irradiation amount or the integrated irradiation amount of the radiation.
Japanese Patent Laid-Open No. 2012-52896 discloses a radiation image capturing apparatus that includes a pixel for capturing a radiation image and a pixel for detecting radiation (a pixel for detecting the start of emission of radiation). The signal of the pixel for capturing a radiation image and the signal of the pixel for detecting radiation are detected via the same signal line.
With the apparatus disclosed in Japanese Patent Laid-Open No. 2012-52896, in order to detect the start of emission of radiation, it is necessary to detect a signal that appears in the signal line in a state in which radiation is being emitted. Here, in the state in which radiation is emitted, the potential of the lower electrode of the pixel for capturing a radiation image changes. Since there is a significant parasitic capacitance between the lower electrode and the signal line, when the potential of the lower electrode of the pixel for capturing a radiation image changes, the potential of the signal line changes due to capacitive coupling (i.e., crosstalk) between the lower electrode and the signal line. Accordingly, in addition to changing due to signals from the pixel for detection radiation, the potential of the signal line also changes due to capacitive coupling with the lower electrode of the pixel for capturing a radiation image. In Japanese Patent Laid-Open No. 2012-52896, there is no acknowledgment of the above-mentioned problem, nor is there any disclosure regarding a countermeasure against such a problem.